The shepherd moon Pan orbits Saturn in the Encke gap while the A ring surrounding the gap displays wave features created by interactions between the ring particles and Saturnian moons.
Pan (17 miles, or 28 kilometers across) maintains the Encke gap through gravitational interactions with ring particles. The wave features in the A ring are generated through interactions between ring particles and moons such as Pan.
This view looks toward the sunlit side of the rings from about 34 degrees above the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on May 11, 2013.
The view was obtained at a distance of approximately 240,000 miles (386,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 111 degrees. Image scale is 1 mile (2 kilometers) per pixel.
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk. — Garrison Keillor
<<Pan (Greek: Πάν) is the second-innermost moon of Saturn. It is a walnut-shaped small moon about 35 kilometres across and 23 km high that orbits within the Encke Gap in Saturn's A Ring. Pan is a ring shepherd and is responsible for keeping the Encke Gap free of ring particles. It was discovered by Mark R. Showalter in 1990 from analysis of old Voyager 2 probe photos and received the provisional designation S/1981 S 13 because the discovery images dated back to 1981. The moon was named on 16 September 1991, after the mythological Pan, who was (among other things) the god of shepherds. This is a reference to Pan's role as a shepherd moon.
The eccentricity of Pan's orbit causes its distance from Saturn to vary by ~4 km. Its inclination, which would cause it to move up and down, is not distinguishable from zero with present data. The Encke Gap, within which Pan orbits, is about 325 km wide.
Cassini scientists have described Pan as "walnut-shaped" owing to the equatorial ridge, similar to that on Atlas, that is visible in images. The ridge is due to ring material that Pan has swept up from the Encke gap.
The Encke Gap contains a ringlet that is coincident with Pan's orbit, indicating that Pan maintains the particles in horseshoe orbits. A second ringlet is periodically disrupted by Pan similarly to how the F Ring is disturbed by Prometheus.>>
Ann wrote:Wow, I can hardly believe that a moon would look like that!!!
Thanks for posting this, Art! (And... yes, the comparison with a flying saucer was appropriate!)
Ann
Dang! I put that thing into a parking orbit thinking it would take centuries for humans to get out there to see it. Didn't count on all your satellites and probes and orbiters and rovers. That's not how we do things where I come from, let me tell you! We boldly go where no one has gone before!
I guess moving it now would really stir up the hornets nest, so I better just leave it. I'm not quite ready to go home yet anyway, though one of your recent elections nearly made me move up the departure date.
Ann wrote:
Wow, I can hardly believe that a moon would look like that!!!
Thanks for posting this, Art! (And... yes, the comparison with a flying saucer was appropriate!)
Dang! I put that thing into a parking orbit thinking it would take centuries for humans to get out there to see it.
You put it into a 'Encke Ring' orbit (and, from the looks of it, it's really gotten dinged up badly).
rstevenson wrote:
Didn't count on all your satellites and probes and orbiters and rovers. That's not how we do things where I come from, let me tell you! We boldly go where no one has gone before! I guess moving it now would really stir up the hornets nest, so I better just leave it.
NASA's next space mission to Saturn will be placing a Denver boot on your vehicle
in order to force payment on your outstanding 'Encke Ring' tickets.
rstevenson wrote:
I'm not quite ready to go home yet anyway, though one of your recent elections nearly made me move up the departure date.
<<The Great Gazoo is a tiny, green, floating alien who was exiled to Earth from his home planet Zetox as punishment for having invented a doomsday machine, a weapon of immense destructive power. His invention was a button which if pressed would destroy the universe in an explosive "ZAM," though he insists he made it on a whim ("I wanted to be the first on my block to have one!") with no intent of using it. Gazoo was discovered by Fred and Barney when his flying saucer crashed; Gazoo recognizes Fred's and Barney's world as prehistoric Earth, implying Zetox banished him through time as well as space. Due to the terms of his exile, he was required to do good deeds for whoever found him first, putting him reluctantly under Fred and Barney's command.
Gazoo refers to Fred and Barney as "dum-dums" and constantly causes problems for them. He can materialize and dematerialize objects, teleport, freeze time, travel through time, and perform other remarkable feats, but when he attempts to help out Fred and Barney, he usually ends up causing even more trouble. Although his powers are frequently described as "magic," they are more likely based on incredibly advanced science, in accordance with the third of Clarke's three laws. The only people who are able to see Gazoo are Fred, Barney, and the children, because they believe in him; animals also can see him.>>
<<Atlas was discovered by Richard Terrile in 1980 (some time before November 12) from Voyager photos and was designated S/1980 S 28. In 1983 it was officially named after Atlas of Greek mythology, because it "holds the rings on its shoulders" like the Titan Atlas held the sky up above the Earth.
Atlas is the closest satellite to the sharp outer edge of the A ring, and was long thought to be a shepherd satellite for this ring. However, now it is known that the outer edge of the ring is instead maintained by a 7:6 orbital resonance with the larger but more distant moons Janus and Epimetheus. In 2004 a faint, thin ring, temporarily designated R/2004 S 1, was discovered in the Atlantean orbit.
High-resolution images taken in June 2005 by Cassini revealed Atlas to have a roughly spherical centre surrounded by a large, smooth equatorial ridge. The most likely explanation for this unusual and prominent structure is that ring material swept up by the moon accumulates on the moon, with a strong preference for the equator due to the ring's thinness. In fact, the size of the equatorial ridge is comparable with the expected Roche lobe of the moon. This would mean that for any additional particles impacting the equator, the centrifugal force will nearly overcome Atlas's tiny gravity, and they will likely be lost.
Atlas is significantly perturbed by Prometheus and to a lesser degree by Pandora, leading to excursions in longitude of up to 600 km (~0.25°) away from the precessing Keplerian orbit with a rough period of about 3 years. Because the orbits of Prometheus and Pandora are chaotic, it is suspected that Atlas's may be as well.>>
